Renal oncocytoma associated with obliterative renal fibrosis. Report of a case with histologic, immunohistochemical, and ultrastructural studies.

We report an unusual case of a renal tumor that showed the classic features of oncocytoma but was wholly encapsulated in a shell of obliterative fibrosis with histologic features identical to those of retroperitoneal fibrosis. Although localized forms of retroperitoneal fibrosis are not uncommonly reported in cases of invasive or metastatic disease, to our knowledge this represents the first report of this process in association with a truly benign tumor of renal epithelial origin.